In many present self-polishing antifouling coating compositions, copper is a main component in the form of cuprous oxides. Copper is an expensive raw material and the environmental effect of copper is under debate. Consequently, there is a growing interest in antifouling coating compositions with reduced copper content or even products free of copper. One option is to exchange cuprous oxide with zinc oxide (e.g. WO 97/00919), however this approach also have its limitations; e.g. high amounts of zinc oxide may have a negative effect on discoloration. Both cuprous oxide and zinc oxide are slightly soluble in seawater and thereby have a strong effect on the polishing properties of the paint coat (Yebra, D. M., Kiil, S., Weinell, C., Dam-Johansen, K. (2006) Dissolution Rate Measurements of Seawater Soluble Pigments for Antifouling Paints: ZnO. Prog. Org. Coat. 56(4), 327-337). On the other hand, non-soluble materials typically have a negative effect on the polishing properties.
Hence, there is generally a need for self-polishing coating compositions where cuprous oxide and/or zinc oxide is partly or fully replaced with other “pigment/filler” constituents, while maintaining the self-polishing properties.
EP 866103 A1 (Nippon Paint) discloses a method for releasing an antimicrobial compound from a matrix. An enzyme and a substrate for the enzyme are incorporated in the matrix.
U.S. Pat. No. 5,770,188 (Nippon Paint) discloses an anti-fouling paint composition containing an enzyme-susceptible resin and a lipid-coated enzyme which is stable in organic solvents and is capable of catalysing the degradation of the resin. It is mentioned that an enzyme-susceptible resin may include starch, and that—in such instanced—α-amylase, β-amylase, glucoamylase and the like may be used as the enzyme.
US 2002/01106361 (Danisco) discloses an anti-fouling composition comprising a surface coating material, an enzyme and an enzyme substrate. One enzyme-substrate combination is represented by amyloglucosidase-starch/hexose oxidase-glucose. The composition may be self-polishing.
WO 2006/002630 A1 (Biolocus) discloses a self-polishing anti-fouling coating composition comprising a hydrolysable polymer composition and a first enzyme having anti-fouling activity. In one embodiment, a second enzyme which is capable of hydrolysing the hydrolysable polymer composition is included.
In view of the above, there is a need for alternative self-polishing coating composition.